1. Field of the Invention
The present invention relates generally to methods for treating and prevention of disorders associated with increased TNF-α and IL-1β by administering therapeutically effective amounts of stearidonic acid.
2. Description of Related Art
Inflammation is the body's response to injuries caused by mechanical damage, infection, or antigenic stimulation, and is therefore a beneficial process for health and survival. However, inflammation can also be induced by inappropriate stimuli such as autoantigen stimulation, which frequently leads to development of autoimmune diseases. Inflammation also can significantly contribute to the pathophysiology of such diseases.
The characteristics of inflammation include heat, redness, pain, and swelling, all of which are at least partly attributable to the effects of cytokines on the local blood vessels. Cytokines are non-antibody proteins secreted by inflammatory leukocytes and some non-leukocytic cells, that act as intercellular mediators. They differ from classical hormones in that they are produced by a-number of tissue or cell types rather than by specialized glands. They generally act locally in a paracrine or autocrine rather than endocrine manner.
Proinflammatory cytokines include tumor necrosis factor, such as TNF-α; interleukins, such as IL-1β, IFN-γ, IL-8, IL-6; including granulyte macrophage colony stimulating factor (GM-CSF); all playing a major role in initiating inflammatory responses and keeping the inflammation process going. Such cytokines, mediators of inflammation, lead to changes in vascular diameter, blood flow, and expression of adhesion molecules on the endothelial cells of local blood vessels, thereby leading to extravasation of immune cells to the sites of inflammation.
For instance, IL-8 acts as a chemoattractant for neutrophils, thus allowing for more efficient extravasation of these cells to the sites of injury. Antibodies blocking against IL-8 have demonstrated the role for IL-8 in the neutrophil associated tissue injury in acute inflammation (Harada et al., Molecular Medicine Today, 2:482, 1996). IL-6 is also a mediator of inflammation, especially in the central nervous system. Elevated levels of IL-6 are found in disorders such as systemic lupus erythematosus, multiple sclerosis, and viral and bacterial meningitis (Gruol et al., Molecular Neurobiology, 15:307, 1997). GM-CSF is a proinflammatory cytokine that is involved in bronchial asthma (Lee, J. R., Coll Physicians Lond, 32:56, 1998). IFN-γ has been associated with increased collagen deposition, which is observed in graft-versus-host disease (Parkman, Curr. Opin. Hematol., 5:22, 1988). The development of insulin-dependent diabetes (Type I) has been correlated with the accumulation of T-cell produced IFN-γ in pancreatic islets (Ablumunits, et al., J. Autoimmun., 11:73, 1998).
TNF-α and IL-1 are synthesized by monocytes and other cells in response to injury, as well as to infectious, inflammatory, or immunologic challenges. These cytokines are involved in a multitude of inflammatory disorders and can cause significant damage through their exerted actions. Among the biological actions of IL-1 are: activation of vascular endothelium, activation of lymphocytes, local tissue destruction, and the promotion of increased access of effector cells to the sites of inflammation. Some of the major effects of TNF-α include increased fluid drainage to lymph nodes and increased vascular permeability, thus leading to increased entry of IgG antibodies, complement, and cells to injured tissues (Charles A. Janeway, Jr., Paul Travers, Mark Walport, and J. Donald Capra, Immunobiology, Fourth Edition, Elsevier Science Ltd/Garland Publishing, 1999). IL-1 and TNF-α often act synergistically, for example, on vascular endothelium and on the synthesis of metabolites of arachidonic acid.
The involvement of TNF-α in a number of diseases has been clinically demonstrated by administering anti-TNF-α monoclonal antibody to patients afflicted with rheumatoid arthritis, Chron's disease, and ulcerative colitis (Rankin E. C. C., et al., British J. Rheum, 35:334–342, 1997, and Stack, W. A., et al., Lancet 349:521–524, 1997). Elevated levels of IL-1 have been demonstrated in patients with inflammatory bowel disease (IBD). Insufficient production of endogenous IL-1ra may contribute to pathogenesis of IBD (Cominelli, et al., 1996, Ailment Pharmacol. Ther., 10, 49, 1996). IL-1 and TNF-α are both involved in periodontal disease (Howells, Oral Dis., 1, 266, 1995). In addition, IL-1, TNF-α, and GM-CSF have been shown to stimulate proliferation of acute myelogenous leukemia blasts (Bruserud, Leukemia Res., 20, 65, 1996). TNF-α and IL-1, together with IL-6 and IL-8, initiate acute phase response observed in fever, malaise, myalgia, etc. (Beisel, Am. J. Clin. Nutr., 62:813, 1995), and are thus commonly observed following trauma or pathogen invasion.
The serious problems associated with septic shock are mostly due to the actions of TNF-α. In septic shock, vasodilation, increased vascular permeability, and blood clotting are initiated by TNF-α and often lead to failure of organs such as kidneys, liver, heart, and lungs. Cachexia, which is a common symptom of prolonged infection or advanced malignancy, results from chronic exposure to TNF-α or IL-6. In addition, animal studies performed in mice and rats have further shown that administration of TNF-α or IL-1 leads to anorexia, weight loss, and depletion of body lipids and proteins within 7 to 10 days (Cerami et al, Immunol Lett., 11:173, 1985; Fong et al., J. Exp. Med., 170:1627, 1989; Moldawer et al., Am. J. Physiol, 254:G450–G456,1988; Fong et al., Am. J. Physiol, 256:R659–R665, 1989; McCarthy et al., Am. J. Clin. Nutr., 42:1179–1182, 1982).
The role of TNF-α and/or IL-1 has been demonstrated in the pathophysiology of many inflammatory disorders. In recent years, new evidence related to the role of inflammation in cardiovascular disease, and particularly in atherosclerosis has started to emerge. This is highly relevant given that cardiovascular disease is the number one cause of mortality in the world. Atherosclerosis is characterized by deposition of plaques that contain cholesterol, lipoid material, and lipophages in large and medium-sized arteries. Formation of plaques often leads to inadequate coronary blood flow to the ventricular myocardium, leading to conditions such as ischemia and pain (angina pectoris) and death of cardiac muscle (myocardial infarction). One such marker of systemic inflammation that is produced in the liver is high-sensitivity C-reactive protein (hsCRP). HsCRP has been shown to be the strongest univariate predictor of the risk of cardiovascular events (NEJM Vol. 342 no. 12:836).
It has been known that oxidative modification of low-density cholesterol plays a role in the deposition of plaques in the arteries. However, according to Paul Ridker, a Harvard cardiologist, it is highly likely that inflammation plays an important part in atherosclerosis by destabilizing plaques, thereby leading to their mobilization through the blood stream. In support of this theory is the fact that aspirin, which has blood thinning and anti-inflammatory properties, decreases the chances of a heart attack even though aspirin has no effect on cholesterol or lipid profile.
It is also known that long chain omega-3 fatty acids such as eicosapentaenoic acid (EPA, 22:5, n-3) and docosahexaenoic acid (DHA, 22:6, n-3), which are found in fish and fish oil, are responsible for many of the health benefits attributed to polyunsaturated fatty acids, including inhibition of inflammation.
Omega-3 (n-3) fatty acids are polyunsaturated fatty acids in which a double bond is located between the third and fourth carbon atom from the methyl end of the fatty acid chain. They include, but are not limited to, α-linolenic acid (ALA, 18:3, n-3), stearidonic acid (SDA,18:4, n-3), eicosapentaenoic acid (EPA, supra), docosapentaenoic acid (22:5, n-3) and docosahexaenoic acid (DHA, supra) and the like. Relatedly, omega-6 fatty acids (“n-6”) have a first double bond at the sixth carbon from the methyl end of the chain; and include, but are not limited to, linoleic acid (LA, 18:2), γ-linolenic acid (GLA, 18:3, n-6), arachidonic acid (AA, 20:4, n-6), and the like. Arachidonic acid is the principal precursor for the synthesis of eicosanoids, which include leukotrienes, prostaglandins, and thromboxanes, and which also play a role in the inflammation process. Administration of an omega-3 fatty acid, such as SDA, has been shown to inhibit biosynthesis of leukotrienes (U.S. Pat. No. 5,158,975).
Omega-3 fatty acids are scarce in a normal Western diet but make up a significant part of fat intake in diets rich in cold-water fish and seal meat. Epidemiological studies-in populations of coastal Eskimo, Japanese, and Dutch populations have shown that a high intake of omega-3 fatty acids correlates with a low incidence of cardiovascular and inflammatory diseases, such as asthma and Type I diabetes mellitus. Thus, a number of studies have demonstrated the health benefits of omega-3 fatty acids. However, it previously was unknown that SDA can be administered to down-regulate TNF-α and IL-1β. Furthermore, as discussed below, the current use of natural and synthetic sources of SDA pose a number of problems.
At present, existing treatments for inflammatory disorders frequently are accompanied by a multitude of issues. For example, since many of the drugs given to treat autoimmune diseases are based on inhibiting a patient's immune system, they also compromise a patient's ability to fight infections. More importantly, these drugs may be accompanied by serious, and sometimes life-threatening side-effects. For example, while corticosteroids (also known as glucocorticoids) such as prednisone and methylprednisone are effective at controlling rheumatoid arthritis, Systemic Lupus Erythematosus (SLE), graft vs. host disease, and a number of other autoimmune diseases, their side-effects include osteoporosis, fluid retention, weight gain, onset or worsening of diabetes, cataracts, and hypertension. Another group of drugs, broadly categorized as immuno-suppressants such as methotrexate, azathioprine, cyclosporine, and leflunomide are also effective at regulating the immune system. However, their side-effects include potential liver problems and low white blood cell count (methotrexate), blood abnormalities (azathioprine), hypertension, loss of kidney function, tremors (cyclosporine), diarrhea, skin rashes, and liver problems (leflunomide). Recent development of anti-TNF-α monoclonal antibodies for treatment of rheumatoid arthritis has proven to be a successful treatment for alleviating the symptoms of the disease, however the administration is via injection, and can be painful and difficult to use.
Accordingly, omega-3 fatty acids could successfully be used to treat a number of inflammatory disorders. However, provision of EPA and DHA, which show great potential for such treatments, can be difficult to obtain or otherwise problematic.
There are several disadvantages associated with commercial production of polyunsaturated fatty acids (PUFAs) from natural sources. Natural sources of PUFAs, such as animals and plants, tend to have highly heterogeneous oil compositions. The oils obtained from these sources therefore can require extensive purification to separate out one or more desired PUFAs or to produce an oil which is enriched in one or more PUFAs. Natural sources also are subject to uncontrollable fluctuations in availability. Fish stocks may undergo natural variation or may be depleted by over-fishing. Fish oils, which contain high levels of EPA and DHA generally have unpleasant tastes and odors. These undesirable attributes may be impossible to economically separate from the desired product, and can render such products unacceptable as food supplements. In addition, animal oils, and particularly fish oils, can accumulate environmental pollutants. Crops which do produce desirable PUFAs, such as borage, have not been adapted to commercial growth and may not perform well in monoculture. Use of microorganisms for production of PUFAs can also present significant problems. For instance, microorganisms such as Porphyridium and Mortierella are difficult to cultivate on a commercial scale. In addition, large scale fermentation of organisms such as Mortierella is expensive.
Dietary supplements and pharmaceutical formulations containing PUFAs can retain the disadvantages of the PUFAs source. Supplements such as fish oil capsules can contain low levels of the particular desired component and thus require large dosages. High dosages result in ingestion of high levels of undesired components, including contaminants. Unpleasant tastes and odors of the supplements can make such regimens undesirable, and may inhibit compliance by the patient. Care must be taken in providing fatty acid supplements, as over-addition may result in suppression of endogenous biosynthetic pathways and lead to competition with other necessary fatty acids in various lipid fractions in vivo, leading to undesirable results. For example, Eskimos having a diet high in ω-3 fatty acids have an increased tendency to bleed (U.S. Pat. No. 4,874,603; Saynor and Varell, Medical Science 8:379 (1980)).
Thus, it is desirable to provide novel and culturally acceptable ways in which to utilize PUFAs to regulate proinflammatory cytokines. The below described invention fulfills this need.